Creating a CUSUM control chart

Plot a CUSUM control chart to determine if a process is in a state of statistical control.

  1. Select a cell in the dataset.
  2. On the Analyse-it ribbon tab, in the Statistical Analyses group, click Process Control, and then click CUSUM
    The analysis task pane opens.
  3. In the Model drop-down menu:
    • If the data are individual observations, select Process variable .
    • If the data are rational subgroups, select Process variable with Subgroups.
  4. In the Process drop-down list, select the quality characteristic variable.
  5. If the data are collected in subgroups, in the Sample size group:
    • If the subgroups are identified by a variable, select Subgroup by identifier variable, and in the Id drop-down list, select the subgroup identifier variable.
    • If the subgroups are a constant size and formed by consecutive number of observations of the process variable, Subgroup size constant, and in the edit box, enter the number of consecutive observations per subgroup.
  6. Optional: If the data are individual observations, in the Id drop-down list, select an identifier variable
  7. In the k and h edit boxes, type the design parameters for the CUSUM chart.
    Note: k and h are specified in multiples of sigma and not in the data measurement units.
  8. Optional: To detect existing out-of-control situations quickly, select the Headstart check box, and in the Headstart h edit box, type the headstart value.

    Typically the headstart h is set to half the h value.

  9. Optional: To standardize the CUSUM statistic, so the control limits are constant regardless of the size of each subgroup, select Standardized plot.
  10. Optional: To reset the value of the CUSUM statistic after each out-of-control signal, select the Reset after out-of-control signal check box.
  11. Optional: To specify known process parameters, select the Known process parameters check box, and then in either or both the Mean and Standard deviation edit boxes, type the known value of the parameter.
  12. Optional: To show the process mean and sigma statistics, select the Show process statistics check box.
  13. Optional: To show the center and control limit statistics, select the Show process control statistics check box.
  14. Click Calculate.